Bug 2547114 (CVE-2026-105239)

Summary: CVE-2026-105239 log4net-windows: log4net: Log record truncation via null byte in EventLogAppender
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Apache log4net. On Windows systems using the EventLogAppender component, logged content containing a null (NUL) byte causes the Windows Event Log entry to terminate prematurely at that character. An attacker who can supply data written to the logs can exploit this vulnerability to truncate log records, concealing critical trailing information such as exception traces and audit fields.
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Description OSIDB Bzimport 2026-10-06 19:54:19 UTC 
Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net.

A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use EventLogAppender are affected.

This issue affects Apache log4net: from 1.2.9 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.